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digitalmars.D.bugs - [Issue 4948] New: std.algorithm.sort asserts unexpectedly with certain comparators

reply d-bugmail puremagic.com writes:
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           Summary: std.algorithm.sort asserts unexpectedly with certain
                    comparators
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: peter.alexander.au gmail.com


--- Comment #0 from Peter Alexander <peter.alexander.au gmail.com> 2010-09-26
14:10:13 PDT ---
The following code asserts unexpectedly when compiled with DMD 2.048 using no
flags.

void main()
{
    alias Tuple!(int, "x", int, "y") V;
    V[] vs = [V(3, 4), V(6, 8)];    
    float arg(V v) { return atan2(cast(float)v.y, cast(float)v.x); }
    bool order(V a, V b) { return arg(a) < arg(b); }
    sort!order(vs);
}

core.exception.AssertError C:\D\dmd2\windows\bin\..\..\src\phobos\std\array.d(356):
Attempting to fetch the front of an empty array

It does not assert when the arg(V) function is replaced to be something more
simple, and only asserts when vs has particular values.

I suspect this has something to do with floating point inaccuracies with atan2,
but haven't looked deep enough into the issue.

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Sep 26 2010
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4948


Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com


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Jan 09 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Brad Roberts <braddr puremagic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Platform|x86_64                      |x86


--- Comment #1 from Brad Roberts <braddr puremagic.com> 2011-02-06 15:40:52 PST
---
Mass migration of bugs marked as x86-64 to just x86.  The platform run on isn't
what's relevant, it's if the app is a 32 or 64 bit app.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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SomeDude <lovelydear mailmetrash.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lovelydear mailmetrash.com


--- Comment #2 from SomeDude <lovelydear mailmetrash.com> 2012-04-22 08:40:00
PDT ---
Note that replacing
    float arg(V v) { return atan2(cast(float)v.y , cast(float)v.x); }
with
    float arg(V v) { return (cast(float)v.y * cast(float)v.x); }
or
    float arg(V v) { return (cast(float)v.y / cast(float)v.x); }
is enough to make the bug disappear...

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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |WORKSFORME


--- Comment #3 from Andrei Alexandrescu <andrei metalanguage.com> 2012-04-22
09:42:49 PDT ---
Works for me on 2.059. I'll also note that arg(v[0]) == arg(v[1]).

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SomeDude <lovelydear mailmetrash.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|WORKSFORME                  |


--- Comment #4 from SomeDude <lovelydear mailmetrash.com> 2012-04-22 10:00:38
PDT ---
I'm sorry but I'm reopening the case: there is no reason for the sort to fail
if two elements are equal. A sort that fails in this case is broken.

Besides, as I've said before, it works with a multiplication or a division,
even with equals elements. It only fails with the atan2 function.

import std.stdio;
import std.typecons, std.algorithm, std.math;

void main()
{
    alias Tuple!(int, "x", int, "y") V;
    V[] vs = [V(6, 8), V(1, 2), V(6, 8), V(5,6)];    
    float arg(V v) { return (cast(float)v.y * cast(float)v.x); }
    bool order(V a, V b) { return arg(a) < arg(b); }
    writeln(sort!order(vs));
}

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--- Comment #5 from Andrei Alexandrescu <andrei metalanguage.com> 2012-04-22
10:43:11 PDT ---
I meant to say it works for me with no assert no nothing. For the last example
the output is:

Tuple!(int,"x",int,"y")(1, 2), Tuple!(int,"x",int,"y")(5, 6),
Tuple!(int,"x",int,"y")(6, 8), Tuple!(int,"x",int,"y")(6, 8)]

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--- Comment #6 from Andrei Alexandrescu <andrei metalanguage.com> 2012-04-22
10:49:24 PDT ---
Rats. That's the output with the multiplication. Using atan2 the output is:

[Tuple!(int,"x",int,"y")(5, 6), Tuple!(int,"x",int,"y")(6, 8),
Tuple!(int,"x",int,"y")(6, 8), Tuple!(int,"x",int,"y")(1, 2)]

That's on OSX Lion/64 bit.

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prev sibling parent d-bugmail puremagic.com writes:
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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |WORKSFORME


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